Roller rail clamp

ABSTRACT

The invention provides roller rail clamp apparatus for use in lifting a rail for operations such as replacement of ballast or resurfacing of a railway. The apparatus comprises parallel pairs of spaced-apart lift roller assemblies mounted to a support for positioning a pair of clamping to a rail of the track, each the lift roller assembly comprising at least one pair of rollers, wherein each the roller of a roller pair rotates on an axis in an essentially vertical plane adjacent a rail and the rollers are on opposite sides of a rail when a lift roller assembly is clamped thereto with the head of the rail releasably retained upwardly of flanges at the lower ends of the rollers; means for adjustably connecting the apparatus to a carrier thereof; a lift mechanism for adjusting the vertical position of the support relative to the carrier of the apparatus; and a tilt mechanism for applying torque about a horizontal axis to linkage between members of a pair of lift roller assemblies.

TECHNICAL FIELD

[0001] This invention relates to equipment used in railway maintenance.More particularly, the invention relates to equipment used for lifting asection of track. Specifically, the invention is concerned withequipment referred to in the art as a “rail clamp”.

BACKGROUND ART

[0002] Railways generally consist of a track supported by a bed ofcrushed rock or gravel, this bed being referred to as “ballast” in theart. Most tracks comprise a pair of rails fixed to lateral members knownas “sleepers” (or in some countries, “cross-ties”). Sleepers are formedfrom steel, timber or concrete.

[0003] There is often a need during railway construction or maintenancefor lifting of the track. For example, replacement of ballast issimplified by lifting the track as a whole to allow access to theballast. When new ballast has been placed on top of a section of track,the track has to be lifted up through the ballast so that it can be ontop of the added ballast. Other instances where track lifting isrequired include tamping and lining operations for resurfacing of arailway. Track realignment often requires lifting of the track whilereplacement of sleepers may also require some degree of track lifting.

[0004] For the efficient execution of the procedures referred to in thepreceding paragraph, the machinery is propelled or drawn along therailway at the highest possible speed consistent with quality, machinewear and tear, and safety requirements. The track lift point thus moveswith the machinery. Special equipment is required for lifting under suchcircumstances, the most usual equipment employed being a “rail clamp”.

[0005] There are two general categories of rail clamps—roller andnon-roller. Roller clamps are able to move along the rail with out beingdisengaged, whereas the non-roller clamp must be opened (disengaged)before being moved. It will be appreciated that only roller rail clampsare suitable for use in conjunction with machinery designed to movealong the railway during operation of the machine. Consequently, theclamps must be capable of holding the lifted section of track—which canhave a down force of the order of 35 tonne—and in addition must becapable of moving along the track. This is achieved solely through thegripping of the heads of the rails by the clamps.

[0006] In moving along a section of track, roller rail clamps can beobstructed. This most frequently occurs through the clamp meeting afishplate or excessive weld flashing at a junction between railsections. If a roller rail clamp is not designed to traverse anobstruction, the rail gripped by a particular clamp can be released withthe potential for release of the entire lifted section. Such a“derailing” of the lifted section can have serious consequencesincluding damage to the track. In addition, the clamps per se can bedamaged.

[0007] A limitation of known roller rail clamps is that they are eitherincapable of traversing obstructions on the rails or have a limitedcapacity to traverse obstructions whilst lifting. There is thus a needfor a roller rail clamp that overcomes the foregoing limitations ofexisting roller rail clamps.

SUMMARY OF THE INVENTION

[0008] The object of the invention is to provide a roller rail clampthat overcomes the limitations referred to in the previous paragraph.

[0009] In a broad format, the invention provides roller rail clampapparatus for use with track comprising a pair of parallel rails, saidapparatus comprising:

[0010] parallel pairs of spaced-apart lift roller assemblies mounted toa support for positioning a pair for clamping to a rail of said track,each said lift roller assembly comprising at least one pair of rollers,wherein each said roller of a roller pair rotates on an axis in anessentially vertical plane adjacent a rail and said rollers are onopposite sides of a rail when a lift roller assembly is clamped theretowith the head of said rail releasably retained between said rollers;

[0011] means for adjustably connecting said apparatus to a carrierthereof;

[0012] a lift mechanism for adjusting the vertical position of saidsupport relative to said carrier of said apparatus; and

[0013] a tilt mechanism for applying torque about a horizontal axis tolinkage between members of a pair of lift roller assemblies.

[0014] The principle embodied by the roller rail clamp apparatus definedin the preceding paragraph is that load bearing is transferred betweenlift roller assemblies when traversing an obstacle in the rails of thetrack to which the apparatus is clamped for lifting. This is achievedthrough applying torque to a member that links the lift rollerassemblies of a pair, the torque being applied about a horizontal axis.Alteration of the slope of the assembly of parallel pairs ofspaced-apart lift roller assemblies can result from this application oftorque and hence the positions of the roller assemblies relative to thehorizontal. This will be explained in more detail below but briefly, ina normal working position on open track, torque on the member linkingthe lift roller assemblies of a pair is such that the rear rollerassemblies are bearing the track. Opening of the front rollers(momentarily) as they traverse an obstacle is sensed and after clearingthe obstacle, the torque is reversed through the action of the tiltmechanism so as to confer load bearing on the front lift rollerassemblies. This allows the rear assemblies to traverse the obstaclewith momentary opening of the rollers. Closure of the rollers on passingthe obstacle is sensed and by way of the tilt mechanism, load bearingreverts to the rear roller assemblies.

[0015] The roller rail clamp apparatus of the invention can be adaptedfor use with any machine where lifting of track for the operation of themachine is required. For example, the apparatus can be part of a machinefor removal of ballast. In such an application, the apparatus is used tosuspend the track above an under-wagon plough that excavates the ballastas the machine moves along the railway. Other applications of theapparatus of the invention include lifting of track through ballastnewly applied over the top thereof, re-alignment of track, andundercutting of track. The apparatus can also be used to stabilise ontrack lifting equipment and mobile work platforms.

[0016] Particular features of the roller rail clamp apparatus will bedetailed below as will optional features and preferments. Broadly,however, the apparatus can be connected to any suitable wagon ormachine-frame. Usually, apparatus is mounted midway between the wheelsof a wagon. However, the apparatus can also be mounted ahead of, behind,or anywhere between the wheels of a wagon. Furthermore, the apparatuscan also be supported by an off track machine such as an excavator,crane or gantry.

[0017] The support for the pairs of lift roller assembliesadvantageously comprises a longitudinal beam for each pair ofassemblies, there thus being two beams in the apparatus that are aboutthe same distance apart as the rails of the track. A crosspiece to whichthey are pivotally mounted to allow tilting of the beams typically linksthe beams. It will be appreciated however that the support can be anyassembly of members that appropriately positions the lift rollerassemblies for clamping to rails yet permits tilting of the pairs ofassemblies.

[0018] The means for adjustably connecting the apparatus to the wagon orequipment carrying it can be any suitable means. For example, theconnection means can be a series of vertical and horizontal slides, adrawbar or a push bar. In place of a drawbar, a parallelogram linkagecan be used. In a preferred form of the apparatus in which the supportfor the lift roller assemblies comprises linked longitudinal beams, theconnecting means is conveniently a drawbar pivotally linked to a wagoncarrying the apparatus. This drawbar is advantageously pivotallyconnected to the crosspiece between the lifting beams so that lateraland some angular movement of the beams is permitted.

[0019] The distance between the lift roller assemblies of each pair isdetermined by the maximum length of the obstacle to be traversed and theintended maximum speed of the machine incorporating the rail clamp. Thatis, the distance between the assemblies must be sufficient to allowtransfer of load bearing from the rear assemblies to the frontassemblies in the time taken for the obstacle to pass therebetween. Forexample, for traversal of a 600 mm long fishplate at a speed of up to 5to 10 km/hr, a minimum distance between the assemblies of a pair isabout 2,000 mm. This is of course very dependant on the speed ofresponse of the tilt mechanism and the load being lifted.

[0020] In a preferred embodiment, each lift roller assembly comprisestwo pairs of rollers. The pairs, when spaced apart within a range of 100to 400 mm, allows traversal of a small obstacle such as a weld flashingwithout the need to transfer load bearing from one assembly to theother. That is, the trailing roller pair of a duplex assembly can carrythe track on opening of the leading pair which closes sufficientlyquickly to carry the track during opening of the trailing roller pair.

[0021] The rollers of the lift roller assemblies are advantageously ofthe non self-locking type and are forced open by the obstacle. Therollers move out and around the obstacle whilst full clamp force ismaintained. There will be some momentary dynamic variation in clampforce as the rollers negotiate the obstacle. However, this is reduced toa minimum by judicious design that may include the use of appropriatelysized, pressurised and located hydraulic accumulators in order tominimise the effect of the momentary dynamics on the net clamping force.The operation of the rollers will be explained in greater detail below.

[0022] Rollers are advantageously flanged at their distal ends. Theflange lies beneath the head of a rail when a pair of rollers is clampedthereabout and can back-up the primary gripping of the head by the rimportion of rollers.

[0023] The lift and tilt mechanisms can be any suitable mechanisms knownto those of skill in the art. For example, lifting and tilting can byway of pulleys, gears, motors or rams or combinations of thesemechanisms. Preferably, hydraulic rams are used to effect lifting andtilting.

[0024] The range of vertical adjustment of the support for the liftroller assemblies is in most instances limited at its maximum by theheight above the normal track level of the chassis of a wagon carryingthe roller lift clamp apparatus and rail stress considerations. Ingeneral, an adjustment range of 100 mm below to 400 above the normaltrack level is adequate. However, the adjustment range will depend on anumber of variables such as rail size, sleeper type, and the particularoperation being undertaken.

[0025] Having broadly described the invention, a non-limiting example ofa roller rail clamp will now be provided with reference to theaccompanying drawings briefly described hereafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is an elevational view of a roller rail clamp according tothe invention.

[0027]FIG. 2 is a plan view of the roller rail clamp shown in FIG. 1.

[0028]FIG. 3 is an end elevation of the roller rail clamp of the earlierfigures with a portion of the drawing in cross-section at A-A of FIG. 2.

[0029]FIG. 4 is a detailed view of the cross-section through the rollersat A-A of FIG. 2.

[0030]FIGS. 5A to 5C are end elevations of the same roller rail clampassembly shown in FIG. 3 with a similar cross-section through the pairof rollers closest the viewer. The assembly components are exploded inFIG. 5A.

[0031]FIGS. 6A to 6F depict the operation of the roller rail clamp ofthe invention.

[0032] In the figures, the same item number is used for a featureincluded in more than one drawing. A particular drawing is notnecessarily to the same scale as other drawings.

BEST MODE AND OTHER MODES OF CARRYING OUT THE INVENTION

[0033] In FIGS. 1 to 3 there is shown roller rail clamp 1 mountedbetween railway wagon 2 only portion of which is shown in these figures(the wagon has been omitted from FIG. 2 for clarity). It will beappreciated that the wagon includes other components such as bogies ateach end thereof and couplings. Equipment such as a system for operatinghydraulic rams for operation of the rail clamp is also associated withthe wagon.

[0034] Roller rail clamp 1 comprises lifting beams 3 and 4, drawbar 5which is linked to the lifting beams by crosspiece 6, and lift rollerassemblies 7 to 10. Drawbar 5 is connected to wagon 2 at 11 in such amanner that the drawbar can pivot in a vertical and horizontal planewith respect to the wagon. The ends of crosspiece 6 are journalled tothe lifting beams at 12 and 13 which allows the pivoting of the liftingbeams. Consequently, the vertical position of lifting beams 3 and 4 canbe adjusted as can the tilt of the lifting beams. The adjustment of thevertical position of the lifting beams is effected by hydraulic liftrams 14 and 15 connected to a crosspiece 16. The tilt of each liftingbeam is independently controlled by hydraulic rams that act between armsextending from the lifting beam and crosspiece 6. Such a tilt ram forlifting beam 4 is indicated at 17 of FIG. 1 where it acts between arms18 and 19. It will be appreciated that a similar assembly is associatedwith lift beam 3.

[0035] Drawbar 5 in addition to being pivotally connected to wagon 2 isalso pivotally connected to crosspiece 6 at 20. This allows lateralmovement of the rail clamp with respect to the wagon. The lateraldisplacement of the lifting beams, and hence the lift roller assemblies,is regulated by an hydraulic ram 21 acting between drawbar 5 and ananchor point 22 on wagon 2. The lateral offset of the lifting beams islimited to about 200 mm. Coupling of lift rams 14 and 15 to crosspiece16 at the ends 23 and 24 thereof is such that some lateral moment ispermitted.

[0036] The ability to laterally displace the lifting beams of the railclamp allows compensation for displacement of the track relative to thecentre line of the wagon such as will occur when the wagon is travellingthrough a curve of small radius.

[0037] At each end of lifting beams 3 and 4 of roller rail clamp 1 thereis fitted a height adjustable guide roller—see items 25 and 26 of FIG. 1and item 27 of FIG. 3. The rollers, 28 to 30, respectively, of theseguide rollers contact the running surfaces of the rails and thus help tomaintain the rail heads in the grooves of the rollers of the lift rollerassemblies (see below). The contact between the rollers 28 and 29 andthe running surface of a rail can be appreciated from FIG. 1 where line31 represents the running surface. It can be further appreciated fromFIG. 3 that rollers are flanged (see item 30) to maintain the guideroller on rail 32.

[0038] The function of the guide rollers is to maintain the rollers ofthe lift roller assemblies in proper contact with the rail head.Depending on the settings of the lift roller assemblies, the lift rollerflanges can move downwardly from snug under the rail head throughcontact between the roller rims and the head of the rail. This isparticularly the case with track consisting of lighter rail material(for example, 41 kg/m rail).

[0039] With regard to the lift roller assemblies, one will now bedescribed with reference to the assembly identified as item 10 in FIGS.1 to 3. However, the features of lift roller assembly 10 are identicalto the other assemblies of roller rail clamp 1.

[0040] Lift roller assembly 10 comprises two pairs of rollers 33 and 35,and 34 and 36, respectively (see FIG. 2 in particular), mounted to innerand outer clamp arms, 37 and 38 respectively. The mounting of therollers to the clamp arms is such that vertical pivoting is possible.This allows individual opening and closing of rollers within a rollerpair for crossing small obstacles. Inner and outer clamp arms 37 and 38are in turn pivotally mounted to an upper carrier 39. Pivoting of uppercarrier 39 is about a horizontal axis to allow for opening and closingof the lift rollers around the rail head. Upper carrier 39 is in turnpivotally mounted to lifting beam 4 through a journal at 40. Thispivotal mounting allows adjustment of the angle of the lift rollerassembly as a whole with respect to the rail to which it is clamped.

[0041] The rollers of the lift roller assemblies are set to be at aslight angle to the support member. This can be appreciated from theelevational view of lift roller assembly 10 in FIG. 1. The angling is byno more than several degrees but this aids passage of a rail through therollers and the clamping action as required, the movement of roller railclamp 1 of FIG. 1 with respect to the track being from right to left.

[0042] It can be appreciated from the partial cross-section of liftroller assembly 10 in FIG. 3 that when the assembly is clamped to rail41, rail head 42 is retained in a cavity formed by the rims and flangesof the opposed rollers. This can be appreciated from the enlargedcross-section presented in FIG. 4 which also gives internal detail ofthe rollers. For clarity, only rollers 34 and 36, and rail 41 are shownin this figure.

[0043] With reference to roller 36 as shown in FIG. 4, this can be seento comprise a shaft 43 which is retained within a housing 44 by abearing plate 45. Additional bearings are provided to handle lateralloading on the shaft, which bearings have been omitted from the drawingfor clarity. A lower portion of shaft 43 extends beyond housing 44 andhas fitted thereto a sleeve 46 which is machined to provide a roller rim47 and a flange 48. With rollers 34 and 36 in the clamping position,head 42 of rail 41 is captive within a cavity 49 formed by rims 47 and50, and flanges 48 and 51, of rollers 34 and 36, respectively.

[0044] It can be appreciated from FIG. 4 that engagement of rail head 42by rollers 34 and 36 is via rims 47 and 50 which contact the sides ofthe head. The high clamp squeeze force applied by the rollers—in theexemplified case hydraulically—allows lifting of the rail by theapparatus. However, as a back-up to the primary roller engagement asdescribed above, flanges 48 and 51 can contact the lower edges of railhead 42.

[0045] Lift roller assembly 10 is shown in greater detail in FIGS. 5A to5C where rollers 34 and 36, clamp arms 37 and 38, upper carrier 39, andpivot point 40 can be seen. The pivoting of clamp arms 37 and 38 withrespect to upper carrier 39 is at horizontal pin joints, the ends ofwhich are items 52 and 53, respectively, of FIG. 5B. Clamp arms 37 and38 are powered by a single hydraulic cylinder 54 connecting the upperends of the arms which serves to open and close the two roller pairs ofthe assembly. The rollers are shown in the closed position about rail 41in FIG. 5B and open in FIG. 5C (rail 41 and hydraulic cylinder 54 havebeen omitted from the latter figure for clarity). As indicated above,the rollers 34 and 36 are connected to the clamp arms by near verticalpivots (not shown in the figures). With reference to roller 34, thevertical pivot is positioned midway between roller 33 (see FIG. 2) androller 34, which rollers are joined by a frame that houses the pivot.The pivot connects the rollers to the clamp arm 37. It will beappreciated that rollers 35 and 36 have the same vertical pivotarrangement as rollers 33 and 34. The vertical pivots allow the rollersof one lift roller assembly to open and close around a small obstaclesuch as a weld flashing while the rollers of the other pair of theassembly remain fully clamped. Upper carrier 39 is pivotally connectedto the lift beam, item 4 of FIGS. 1 to 3, by a near horizontal pin at40. It will be appreciated that there is considerable scope foradjustment of angles and positioning of the assembly because of thesepivots. The degree of load sharing between the roller pairs of liftroller assembly 10 can thus be varied by adjustment of a constraintapplied to the motion of the assembly about pin 40. This enables theangle of the rollers to be set to actual operating conditions.

[0046] The lift roller assemblies on each of lifting beams 3 and 4 are2.0 m apart measured from pivot point to pivot point of the supportmembers. The pairs of rollers of each assembly are 500 mm apart at theiraxes. Each roller has a diameter of 230 mm at the flange. Theexemplified roller rail clamp is suitable for lifting track comprising41 to 60 kg/m rails and can be used in machines which operate at up toabout 12 km/hr.

[0047] Operation of the roller rail clamp, and additional features ofthe device, will now be given with reference to FIGS. 6A to 6F. Forclarity the track—or more specifically a rail thereof—on which theroller rail clamp is operating is represented as a single line below theclamp. In actual operation, the rail would of course pass through theroller assemblies. For illustrative purposes, a fishplate constitutesthe obstruction. This is represented as a filled box in the linerepresenting the rail. The working direction of the machine carrying theroller rail clamp is from right to left.

[0048] In FIG. 6A, there is shown roller rail clamp 1 in the normalworking position—that is, clamped to a section of track with the trackelevated—beneath a machine 55 only portion of which is shown in thefigure. As rail clamp 1 is in the normal position, trailing lift rollerassembly 10 is higher than leading lift roller assembly 9 due to tiltingof the lifting beams under the action of hydraulic ram 17 of the tiltmechanism. Lift roller assembly 10 is thus load bearing. Leading liftroller assembly 9 is nevertheless clamped to a rail of the track onwhich machine 55 is operating, which rail is represented by line 56. Therail clamp is approaching a fishplate 57 in the rail.

[0049] In FIG. 6B, the leading lift roller assembly 9 has contactedfishplate 57 effecting opening of the rollers so that the assembly cantraverse the fishplate. The track is still suspended, however, beingheld by the trailing lift roller assembly 10.

[0050] A sensor in lift roller assembly 9 detects opening and subsequentclosing of the rollers as they pass over fishplate 57. Upon sensing theopening of roller assembly 9, the control program takes no externalaction but prepares to respond with a tilt rear when it senses thatroller assembly 9 has cleared the fishplate. Note that in FIG. 6C thefishplate 57 is partially clear of roller assembly 9. No action is takenat this stage other than readiness for the full closing of rollerassembly 9 when it is fully clear of the fishplate.

[0051] Upon sensing that roller assembly 9 has fully closed afterpassing over fishplate 57, a programmable logic control circuit actuateshydraulic ram 17 of the tilt mechanism to tilt the lifting beams so thatleading lift roller assembly 9 is higher than trailing assembly 10 asshown in FIG. 6D. This transfers the load to lift roller assembly 9. Atthis stage, the fishplate obstruction 57 is between lift rollerassemblies 9 and 10.

[0052] In FIG. 6E, trailing lift roller assembly 10 has contactedfishplate 53 effecting opening of the rollers so that the assembly cantraverse the obstruction. As in FIG. 6B, despite opening of the rollersof one of the lift roller assemblies, the track remains suspended beingretained by the now load bearing leading lift roller assembly 9.

[0053] In FIG. 6F, after traversing fishplate 53, closing of the rollersof lift roller assembly 10 is sensed, hydraulic ram 17 is activated, andthe lifting beams are tilted to return the trailing lift roller assemblyto a higher, and load bearing, position as shown in FIG. 6A. This is thenormal working position with the roller rail clamp ready to traverse thenext obstacle.

[0054] In the preceding illustration, reference has only been made tothe lift roller assemblies visible in the drawings. It will beappreciated that the sequence of events described above applies to thelift roller assemblies on the lifting beam behind the visible liftingbeam. Furthermore, each lifting beam has its own tilt cylinder so thatthe lifting beams operate independently over fishplates and otherobstacles.

[0055] It will be appreciated that many changes can be made to theroller lift clamp and use thereof as exemplified above without departingfrom the broad ambit and scope of the invention.

[0056] The term “comprise”, or variants thereof such as “comprising” or“comprised”, is used herein to denote the inclusion of a stated integeror integers, unless is the context of usage an exclusive interpretationof the term is required.

1. Roller rail clamp apparatus for use with track comprising a pair ofparallel rails, said apparatus comprising: parallel pairs ofspaced-apart lift roller assemblies mounted to a support for positioninga pair for clamping to a rail of said track, each said lift rollerassembly comprising at least one pair of rollers, wherein each saidroller of a roller pair rotates on an axis in an essentially verticalplane adjacent a rail and said rollers are on opposite sides of a railwhen a lift roller assembly is clamped thereto with the head of saidrail releasably retained between said rollers; means for adjustablyconnecting said apparatus to a carrier thereof; a lift mechanism foradjusting the vertical position of said support relative to said carrierof said apparatus; and a tilt mechanism for applying torque about ahorizontal axis to linkage between members of a pair of lift rollerassemblies for transferring load bearing from one said lift rollerassembly to the other said lift roller assembly of a said pair, whereinload transfer from the load-bearing lift roller assembly occurs afteropening and subsequent closing of the non load-bearing lift rollerassembly.
 2. The apparatus according to claim 1, wherein said supportfor said lift roller assemblies comprises a longitudinal beam for eachpair of assemblies, the longitudinal beams being spaced apart by across-piece to which said beams are pivotally mounted.
 3. The apparatusaccording to claim 2, further comprising a height-adjustable guideroller at each end of said beam which in use contacts the runningsurface of a said rail.
 4. The apparatus according to claim 1, whereinsaid means for adjustably connecting said apparatus to a carriertherefor is a series of vertical and horizontal slides, a drawbar, apush bar, or a parallelogram linkage.
 5. The apparatus according toclaim 1, wherein said lift and tilt mechanisms comprise pulleys, gears,motors or rams, or any combination thereof.
 6. The apparatus accordingto claim 1, wherein said means for adjustably connecting said apparatusto said carrier comprises a drawbar, and said lift and tilt mechanismscomprise hydraulic rams.
 7. The apparatus according to claim 1, whereina mechanism is provided for lateral adjustment of said apparatusrelative to said carrier.
 8. The apparatus according to claim 7, whereinsaid mechanism comprises at least one hydraulic ram extending betweensaid carrier and said support for said lift roller assemblies.
 9. Theapparatus according to claim 1, wherein said carrier is a wagon,excavator, crane or gantry.
 10. The apparatus according to claim 1,wherein each lift roller assembly comprises two pairs of spaced apartrollers.
 11. The apparatus according to claim 10, wherein inner andouter rollers of said pairs are pivotally mounted, respectively, toinner and outer clamp arms, wherein said pivotal mounting allows openingand closing of the rollers of a pair.
 12. The apparatus according toclaim 11, wherein said inner and outer clamp arms are pivotally mountedto a carrier therefor, wherein said pivotal mounting allows opening andclosing of the rollers of the pairs of a said lift roller assembly. 13.The apparatus according to claim 12, wherein said clamp arm carrier ispivotably mounted to said support to allow adjustment of the angle of asaid lift roller assembly comprising said roller pairs.
 14. Theapparatus according to claim 1, wherein each said roller is flanged atits distal end.
 15. The apparatus according to claim 1, wherein a rollercomprises a shaft retained within a housing by a bearing plate at theupper end of said shaft, and wherein the lower end of said shaft extendsout of said housing and has fitted thereto a sleeve which is machined toprovide a roller rim.
 16. The apparatus according to claim 15, whereinsaid sleeve is further machined to provide a distal flange.
 17. Theapparatus according to claim 1, wherein lift roller assemblies includesensors to detect opening and closing of the rollers of a said pair. 18.The apparatus according to claim 1, wherein a programable logic controlcircuit is provided to control tilting of said support for a pair oflift roller assemblies to transfer load bearing between leading andtrailing assemblies.
 19. The apparatus according to claim 1, whereinsaid rollers of a said pair are non self-locking.
 20. Roller rail clampapparatus for use with track comprising a pair of parallel rails, saidapparatus comprising: parallel pairs of spaced-apart lift rollerassemblies pivotably mounted to a beam for positioning a pair forclamping to a rail of said track, the beams of said pairs beingpivotally connected to a crosspiece and each said lift roller assemblycomprising two spaced apart pairs of rollers, wherein each said rollerof a roller pair rotates on an axis in an essentially vertical planeadjacent a rail and said rollers are on opposite sides of a rail when alift roller assembly is clamped thereto with the head of said railreleasably retained upwardly of flanges at the lower ends of saidrollers, and wherein said rollers of a said pair are non self-locking toallow opening thereof on contacting an obstacle; a drawbar foradjustably connecting said apparatus to a wagon with which saidapparatus is associated; an hydraulic ram extending between said wagonand each said beam for adjusting the vertical position of a said beamrelative to said wagon; and an hydraulic ram extending between saidcrosspiece and a said beam for applying torque about a horizontal axisrelative to said beam for transferring load bearing from one said liftroller assembly to the other said lift roller assembly of a said pair,wherein load transfer from the load-bearing lift roller assembly occursafter opening and subsequent closing of the non load-bearing lift rollerassembly.